Fault geometry and slip distribution of the 1943 Tosya Earthquake rupture, North Anatolian Fault, Turkey

The North Anatolian Fault (NAF) ruptured in a sequence of large earthquakes between 1939 and 1999, generally progressing from east to west. The November 26, 1943 Tosya earthquake (Mw:7.6), which is second largest event in this sequence, produced 280 km-long multi-segment surface faulting along the northward arc on the central part of the NAF. The event nucleated near the western end of the rupture and propagated towards to the east. However, fault geometry and slip distribution of the 1943 rupture, which provide data to understand fault segmentation and recurrence of the paleo-events for multi-segment faulting, are poorly known. There is no detailed data for segment structure of the rupture. The amount of the surface slip associated with the 1943 event varied between 1.0 and 4.0 m according to previous studies. We performed a serial geomorphologic and geological investigation along the rupture to determine detail fault geometry and slip distribution. In this study, the 1943 rupture was mapped in scale of 1:25 000 using the areal photos in scale of 1:10,000 and tectonic landforms were identified and displacements were measured on the 60 localities along the rupture. The 1943 rupture was divided into nine segments based on slip distribution and fault jogs such as step-overs and bends. The rupture is seperated from the 1944 rupture by a restraining stepover, however, the eastern termination of the rupture overlapped with the 1942 event for the extent of 7 km. In general, changes of the fault direction within the rupture orientation were observed near the restraining bend or stepovers which varies from 50 to 110. Average slip along the sections of the rupture is not uniform. The amount of average slip along the entire rupture is 3.8 m. and the maximum slip of 6.0 m was measured on the Havza segment. The body segments range from 28 to 40 km-long and their average slip varies 3.3 and 4.7 m. Our data indicate that amount of the dextral slip relevant to 1943 Tosya earthquake is larger than previous studies: there is no slip gap along the 1943 earthquake segment within large earthquakes sequence occurred during the 20th century along the NAF. Additionaly, comparision of the slip distribution on the surface ruptures formed in the sequence between the 1943 and 1999 earthquakes shows that average slip along the central and western NAF are rather uniform and do not decrease steeply westward.